Touchscreens have become ubiquitous for computer interface, and are used in mobile phones, tablets, laptop computers, bank kiosks, and many other applications and devices. Touchscreens are able to detect the location of a user's finger in contact with the screen. The detected location then can be used by a computer program to respond to the user's command as expressed by his or her touch, such as to move a graphical object that is visible on the screen or to select a button or menu item.
Usually the touch sensitive screen is transparent and is combined with a visual display so that the user may imagine that he or she is touching or pointing to the objects that are visually portrayed. There are two flows of information involved: visual information from a computer to the user, and touch information from the user to a computer.
Less common is the other direction of conveyance of touch information, in which the user can employ his or her sense of touch to receive information from a computer. This could support the user's perception of edges or textures, or even apparent bumps or depressions of the surface.
The facility to convey touch information to the user is called haptics. A contemporary form of haptics is accomplished by producing vibrations of a handheld device. A user may imagine the vibrations to be originating in his or her interaction with icons or other graphical features portrayed on a visual display. Going beyond vibrational haptics, the term surface haptic display refers to touchscreens in which forces can be generated by the screen and exerted on the user's fingertip at the point that it contacts the screen.
If a touchscreen can separately detect the location of more than one finger in contact with the screen at the same time, this is known as “multitouch.” If a surface haptic display can produce different forces on more than one finger in contact with the screen at the same time, this is known as “multihaptics.”
A challenge for surface haptic display is to find ways for a touchscreen, which is usually made of glass, to be able to exert forces on a fingertip that is touching it. The forces must be under software control. Further, the mechanism of force production must not interfere with detection of the location of a fingertip that is touching the screen. Additionally the mechanism of force production should be reasonably transparent, so that a visual display under the touchscreen is not obscured.
One way of accomplishing surface haptic display is to use electrostatic attraction to create forces on a user's fingertip. Transparent electrodes, such as indium tin oxide (ITO), are placed beneath the surface of a touchscreen, which typically is made of glass. The electrodes are charged to a potential relative to that of a user's finger. The electrostatic attraction between the electrode and the user's fingertip increases the contact force between fingertip and glass, and therefore, also increases the frictional force that the user must overcome to move his or her finger across the glass. The user perceives the increased frictional force, which can be modulated under software control to represent icons, textures, edges, and other haptic effects. The force of electrostatic attraction depends on many factors including the potential difference (voltage), surface area, distance between surfaces attracted, frequency of alternation of the sign of the voltage, and the dielectric constant of the material between them.
An object of the disclosure is to provide capacitive sensing of the position of one or more fingers in contact with a touchscreen and/or to exert haptic forces on one or more fingers in contact with a touchscreen.